A significant contribution of atmospheric contamination from automobile engines is in the form of unburned hydrocarbons and carbon monoxide at speeds of 30 mph or lower, when the automobile engine is in the idle, cruise, acceleration and deceleration operating modes. Further, it has been found that significant contributions to atmospheric contamination by oxides of nitrogen are produced from automobile engines when operating in this just mentioned range, as well as, at high speed cruise modes. The contaminants discharged from automobile engines can be reduced by retarding the spark of the engine. That is, by causing each of the spark plugs to fire later (in relation to the time that the associated piston is at top dead center) than the time at which the manufacturers design the engine to have the spark plugs fire. The automobile manufacturers design the engines to have a maximum power output; however, said maximum output comes with the penalty of excessive emissions.
Merely retarding the spark will not solve the problems--if the spark is merely retarded--there will be a problem of potential overheating at idle speeds, and significant lss of fuel economy at the higher speeds. Accordingly, the spark must be retarded at only certain speed levels in order to minimize the exhaust emissions while avoiding significant degradation of fuel economy, as well as, avoiding overheating at idle speeds.
There is the additional problem that any units placed under the hood of an automobile engine must be capable of operating over a wide range of temperatures.
In addition to the problem of selectively retarding the spark at the desired times-- in order to be economically feasible--the system must be of low cost manufacture, and must be adaptable to a wide range of cars. In addition, the system must be capable of being installed prpoerly by personnel of limited training, then work properly and reliably for long periods of time.